As many as 60 percent of Americans do not engage in regular physical activity and 25 percent are completely inactive. The risk of cardiovascular disease is almost doubled among people who are physically inactive, comparable to the risks associated with increased systolic blood pressure, cigarette smoking, and elevated serum cholesterol. To make an impact on physical activity prevalence at the population level requires a research focus at the interface between clinical efficacy trials and large-scale dissemination studies. Studies at this interface must use proven interventions that are simultaneously effective and cost-efficient. Such interventions are the focus of this proposal. The objective of this study is to determine the differential effect of intervention delivery channel (phone versus print versus wait list control) on physical activity adoption and maintenance in previously sedentary adults. Both delivery channels have been found to be effective, but telephone-based interventions require more commitment on the part of the subjects and are more labor intensive than print-based interventions. Thus, we will conduct a randomized controlled clinical trial comparing three groups: 1) telephone-based motivationally- tailored individualized feedback; 2) print-based, motivationally- tailored individualized feedback; 3) minimal contact waiting list control condition (receive intervention after 12 months as controls). Two hundred and twenty-eight healthy, sedentary women and men ages 18-65 will be randomly assigned to one of the two interventions or the waiting list control condition. The two intervention arms will be matched with respect to frequency and content of contact. Data will be collected at baseline, 6, and 12 months using well-established physical activity and physical performance measures, as well as a comprehensive set of psychosocial questionnaires. Our primary hypothesis is that individuals randomized to either phone or print conditions will exhibit significantly higher levels of phys ical activity participation at 6 and 12 months than individuals in the waiting list control condition. And, in addition, that subjects randomized to the telephone condition will exhibit significantly higher levels of physical activity participation at 6 and 12 months than those in the print condition. Additional questions of interest include evaluation of the cost-effectiveness of the two intervention delivery approaches, each in relation to each other and to the wait list control group and examination of potential moderators and mediators of the intervention-physical activity relationship. This study will contribute important information regarding the relative efficacy and cost-effectiveness of two interventions, each of which can be utilized for widespread public health dissemination.